The invention relates to industrial control systems including programmable controllers, and in particular to an industrial control system employing utility programs such as graphical editors and display programs.
Industrial control systems, such as those described in U.S. Pat. Nos. 3,810,110; 3,942,158; 4,165,534; and 4,442,504, are typically centralized, general-purpose computers that may be connected to industrial equipment through I/O (input/output) modules to operate and control the industrial equipment according to a stored control program. The stored control program runs in real-time to provide outputs to the controlled process as electrical signals connected to actuators and the like, the outputs being based on the logic of the control program and inputs received from sensors on the controlled process.
The demands of real-time processing have historically required a special purpose control-computer capable of rapidly processing the required large amounts of input and output data. Frequently, the control program for such special computers is written in a relay ladder language adapted to the demands of real-time control. In relay ladder logic, the input and output signals may be represented graphically as contact symbols and coil symbols arranged in a series of rungs spanning a pair of vertical power rails.
Often a separate computer is used to write and edit the control program using these graphical symbols. The completed control program is converted to an executable file and loaded into the control-computer for execution.
During execution of the control program, peripheral-computers may communicate with the control-computer directly or through a network to execute other programs to display a real-time animation of the program or of the operation of the controlled equipment. These programs, not necessary for the core function of the industrial control system, but assisting in the development, troubleshooting or monitoring of the control process, will generally be referred to as utility programs.
With the increasing processing power of general purpose "desktop" computers, and in particular those based on microprocessors manufactured by the Intel Corporation, special purpose control-computers may no longer be required for many low-end control applications. "Soft PLC" (programmable logic controller) programs exist that allow a high-end desktop computer, often with multiple processors, to simulate the operation of a special purpose control-computer. Such soft PLC programs execute ladder logic type control programs and control I/O modules to communicate control signals between the desktop computer and the controlled process.
In such soft PLC systems, the peripheral-computers may also be desktop computers.
The large installed base of desktop computers has resulted in powerful and inexpensive computer languages and development systems using desktop operating systems, principally the Windows graphical operating system manufactured by Microsoft Corporation. The utility programs executed by the peripheral-computers, and the soft PLC program itself, are conventionally written using these desktop languages and development systems. The resulting utility programs make extensive use of graphical icons and symbols and require substantial computer resources in terms of memory and processing power to run.
Because of the rigors of the industrial environment, specialized versions of desktop computers, hardened to factory conditions, may be used. Ideally, these hardened desktop computers, when used as peripheral-computers, omit certain components of the desktop computer used to run the soft PLC program, for example, high-speed processors, extra memory and disk drives. These components are costly, create cooling and reliability problems in the field, and may, in the case of disk drives, reduce the ruggedness of the peripheral-computer.
Unfortunately, the latest utility programs created with the desk top operating systems may not operate with reduced component computer systems used as peripheral-computers.